Iron

The serum iron test is used to measure the amount of iron that is in transit in the body – the iron that is bound to transferrin in the blood. Along with other tests, it is used to help detect and diagnose iron deficiency or iron overload. Testing may also be used to help differentiate various causes of anemia.

The amount of iron present in the blood will vary throughout the day and from day to day. For this reason, serum iron is almost always measured with other iron tests, including ferritin, transferrin, and calculated total iron-binding capacity (TIBC) and transferrin saturation.

Serum iron tests may be ordered as follow-up tests when results from a complete blood count (CBC) show that a person’s hemoglobin and hematocrit are low and their red blood cells are smaller and paler than normal (microcytic and hypochromic), suggesting iron deficiency anemia even though other clinical symptoms may not have developed yet.

Testing may be ordered when a person develops signs and symptoms of anemia, such as :

• Chronic fatigue/tiredness
• Dizziness
• Weakness
• Headaches
• Pallor

Testing may be ordered when iron overload is suspected. Signs and symptoms will vary from person to person and tend to worsen over time. They are associated with iron accumulation in the blood and tissues. These may include:

• Joint pain
• Fatigue, weakness
• Lack of energy
• Abdominal pain
• Loss of sex drive
• Organ damage, such as in the heart and liver

When a child is suspected to have ingested iron tablets, a serum iron test is ordered to detect and help assess the severity of the poisoning.

Iron tests may also be ordered periodically when iron deficiency or overload is being treated to evaluate the effectiveness of treatment.

Serum iron levels are often evaluated in conjunction with other iron tests. A summary of the changes in iron tests seen in various diseases of iron status is shown in the table below.

Iron deficiency
The early stage of iron deficiency is the slow depletion of iron stores. This means there is still enough iron to make red cells but the stores are being used up without adequate replacement. The serum iron level may be normal in this stage, but the ferritin level will be low.

As iron deficiency continues, all of the stored iron is used and the body tries to compensate by producing more transferrin to increase iron transport. The serum iron level continues to decrease and transferrin and TIBC and UIBC increase. As this stage progresses, fewer and smaller red blood cells are produced, eventually resulting in iron deficiency anemia.

Iron overload
If the iron level is high, the TIBC, UIBC and ferritin are normal and the person has a clinical history consistent with iron overdose, then it is likely that the person has iron poisoning. Iron poisoning occurs when a large dose of iron is taken all at once or over a short period of time. Iron poisoning in children is almost always acute, occurring in children who ingest their parents’ iron supplements. In some cases, acute iron poisoning can be fatal.

A person who has mutations in the HFE gene is diagnosed with hereditary hemochromatosis. However, while many people who have hemochromatosis will have no symptoms for their entire life, others will start to develop symptoms such as joint pain, abdominal pain, and weakness in their 30’s or 40’s. Men are affected more often than women because women lose blood during their reproductive years through menstruation.

Iron overload may also occur in people who have hemosiderosis and in those who have had repeated transfusions. This may occur with sickle cell anemia, thalassemia major, or other forms of transfusion-dependent anemia. The iron from each transfused unit of blood stays in the body, eventually causing a large buildup in the tissues. Some people with alcoholism and with chronic liver disease also develop iron overload.

Recent consumption of iron-rich foods or iron supplements can affect test results, as can recent blood transfusions.

Normal iron levels are maintained by a balance between the amount of iron taken into the body and the amount of iron lost. Normally, a small amount of iron is lost each day, so if too little iron is taken in, a deficiency will eventually develop. Unless a person has a poor diet, there is usually enough iron to prevent iron deficiency and/or iron deficiency anemia in healthy people.

In certain situations, there is an increased need for iron. Persons with chronic bleeding from the digestive tract (usually from ulcers or tumors such as colorectal cancer) or women with heavy menstrual periods will lose more iron than normal and can develop iron deficiency. Women who are pregnant or breast feeding lose iron to their baby and can develop iron deficiency if not enough extra iron is taken in. Children, especially during times of rapid growth, may need extra iron and can develop iron deficiency. Iron deficiency can also be seen in malabsorption diseases such as celiac disease.

Low serum iron can also occur in states where the body cannot mobilize and use storage iron properly. In many chronic inflammatory conditions, especially in cancers, autoimmune diseases, and with chronic inflammations or chronic infections (including AIDS), the body cannot properly use iron to make more red cells. Under these conditions, production of transferrin decreases, and serum iron is low because little iron is being absorbed from the gut and storage iron can’t get mobilized, and ferritin increases.

Iron deficiency refers to a decrease in the amount of iron stored in the body, while iron deficiency anemia refers to a drop in the number of red blood cells (RBCs), hemoglobin and hematocrit caused by not having enough stored iron (there are many other causes of anemia). It typically takes several weeks after iron stores are depleted for the hemoglobin level to decrease and production of RBCs to be affected and for anemia to develop. There usually are few symptoms seen in the early stages of iron deficiency, but as the condition worsens and blood levels of hemoglobin and RBCs decrease, ongoing weakness, pallor, and fatigue can eventually develop.

As your iron continues to be depleted, you may have shortness of breath and dizziness. If the anemia is severe, chest pain, headaches, and leg pains may occur. Children may develop learning (cognitive) disabilities. Besides the general symptoms of anemia, there are certain symptoms that are characteristic of iron deficiency. These include dysphagia, pica (cravings for specific substances, such as ice, corn starch, licorice, chalk, dirt, or clay), a burning sensation in the tongue or a smooth tongue, sores at the corners of the mouth, and spoon-shaped fingernails and toenails.

The form of iron that is easiest for the body to absorb is found in meats and eggs. Other iron-rich sources include: green leafy vegetables (such as spinach, collard greens, and kale), wheat germ, whole grain breads and cereals, raisins, and molasses.

The people who typically need iron supplements are pregnant women and those with documented iron deficiency. People should not take iron supplements before talking to their healthcare practitioner as excess iron can cause chronic iron overload. An overdose of iron pills can be toxic, especially to children.

Iron deficiency anemia comes on gradually. When your rate of iron loss exceeds the amount of iron you absorb from the foods you eat or supplements, iron stores are slowly used up. At this stage, ferritin will be low, but serum iron and TIBC are usually normal and there is no anemia. As the iron deficiency worsens, serum iron levels fall, TIBC and transferrin rise, and anemia starts to develop. With prolonged or severe iron deficiency, the red cells become small and pale due to decreased hemoglobin levels. Reticulocyte count also decreases.

Yes. Every time you donate a pint of blood, your body loses some iron. The level of ferritin, which is a reflection of the total amount of storage iron in the body, drops with each donation and then returns to normal over time. Other tests, such as serum iron and TIBC, are not as affected by blood donation.

Your doctor may suspect that you are not absorbing the iron you need from your supplements and your diet, so may ask that you have your iron level checked shortly after you take your iron supplement. If you take iron and then have an abnormally low test result, you may have an underlying condition affecting the absorption of iron. You may need to be treated for the condition causing the malabsorption for your iron levels to return to normal.